WL#5420: PERFORMANCE SCHEMA TABLE LOCK WAIT SUMMARY

This aggregation summarizes data obtained with the TABLE LOCK instrumentation,
see WL#5371 PERFORMANCE_SCHEMA Instrumenting Table Locks
Target audience
* Server core developers
Implementers of the server itself, or implementers of storage engines,
do not have direct control on which MySQL user application locks which user table,
so the data provided by this instrumentation can not be used to tune directly
the server.
When implementing changes to the server table locking code however,
server developers will then be able to use the results on this instrumentation
to evaluate the overall impact of a server change on an end user application,
when doing benchmarks.
* Application developers
Application developers writing queries against the database server to implement
an application are the primary target audience for this instrumentation.
Application developers are expected to use the results of this instrumentation
to change how the application issues queries against the database,
and uses locks against tables, to minimize the application footprint on the server,
and improve the application performances / scalability.
* Production engineers
Production engineers monitoring the impact of applications against a database
server are the secondary audience for this instrumentation.
Production engineers are expected to use the results of this instrumentation
to monitor and assess the impact of an application on the whole system during
deployment.
For example, an application doing little table io but locking tables for a long
time could have a negative impact on existing applications already deployed,
and this impact will be visible with the instrumentation provided.
Without table lock instrumentation, this impact will be un accounted for,
and performance drops due to locking will be harder to identify.